Methicillin-Resistant Staphylococcus aureus
(MRSA), 2000

Strains of Staphylococcus aureus that are resistant to methicillin
(and possibly other antibiotics) are referred to as methicillin-resistant
Staphylococcus aureus (MRSA). Such strains were first recognized
in the United States in the late 1960s. Established risk factors for MRSA
include recent hospitalization or surgery and residence in a long-term
care facility.

In 1997, MDH began receiving unsolicited reports from several health
care facilities in Minnesota describing increasing numbers of healthy
young patients presenting with infections caused by MRSA. Many of these
patients appeared to have none of the established risk factors for MRSA
infection. Although most of the reported infections were not severe, some
resulted in hospitalization or death. A review of the scientific literature
indicated that MRSA infection among persons with no apparent risk factors
was unusual. The infections being reported in Minnesota appeared to have
been acquired in the community rather than in the health care setting,
thereby suggesting a possible change in the epidemiology of MRSA. The
phenomenon of community-acquired MRSA (CA-MRSA) also was being reported
elsewhere in the U.S. and the world. An article by MDH authors and others
reported the deaths of four children from Minnesota and North Dakota due
to CA-MRSA [MMWR 1999;48(32):707-710].

In an effort to determine the incidence of CA-MRSA in Minnesota, MDH
initiated active surveillance in January 2000 at 12 sentinel hospitals
statewide. The hospitals (six in the seven-county metropolitan area and
six in greater Minnesota) were selected to represent various geographic
regions of Minnesota. These facilities were asked to submit case reports
and MRSA isolates to MDH for all cases of MRSA (both community-acquired
and health care-associated) identified at their facilities during 2000.
The purpose of this surveillance system included monitoring the incidence
of CA-MRSA infections in Minnesota, identifying possible risk factors
for CA-MRSA, and identifying the antibiotic susceptibility patterns and
genetic subtypes of MRSA isolates submitted to MDH.

To meet the provisional diagnosis of CA-MRSA as defined for the MDH surveillance
system, a patient must not have had: a positive culture for MRSA from
any specimen obtained more than 48 hours after admission to a hospital
(if admitted); history of MRSA infection or colonization; or, hospitalization,
surgery, residency in a long-term care facility, hemodialysis or peritoneal
dialysis, or indwelling percutaneous devices or catheters within the past
year.

During 2000, 1,164 cases of MRSA infection were reported by the 12 sentinel
hospitals. Eleven percent of these cases were determined to be community-acquired,
85% were health care-associated, and 3% were of unknown origin. The MDH
Public Health Laboratory received MRSA isolates from 932 (80%) cases and
completed genetic subtyping on 338 (29%) of these isolates. CA-MRSA patients
were, on average, younger than patients with health care-associated MRSA
(23 years vs. 68 years, respectively) and more likely to have MRSA isolated
from a skin site (74% vs. 40%, respectively). In addition, very few of
the CA-MRSA patients were health care workers or had household members
who were health care workers. The data also confirmed that most CA-MRSA
isolates had genetic subtype and antibiotic susceptibility patterns that
were distinct from health care-associated MRSA isolates. CA-MRSA isolates
typically belonged to a particular clonal group and generally were susceptible
to all of the following drugs: ciprofloxacin, clindamycin, gentamicin,
tetracycline, and trimethoprim-sulfamethoxazole. These findings support
the theory that CA-MRSA bacteria have not "escaped" from the healthcare
setting, but rather have evolved independently and represent a change
in the epidemiology of MRSA.